In recent years, a CMOS (Complimentary Metal Oxide Semiconductor) image sensor has attracted attention as solid-state image sensor (image sensor) in place of a CCD.
This is because the CMOS image sensor has overcome problems below.
In other words, a dedicated process is needed for manufacturing CCD pixels, and a plurality of power-supply voltages are needed for operation thereof, and further, a plurality of peripheral ICs are needs to be combined to operate.
Various problems including that a system may be complicated very much in a case of such a CCD are overcome by the CMOS image sensor.
The CMOS image sensor can be applied with a process similar to that for a general CMOS type integrated circuit and can be driven by a single power supply, and further an analog circuit and logic circuit using a CMOS process can be arranged in the same chip an identical in a mixed manner.
For this reason, the CMOS image sensor has a plurality of great advantages that the number of the peripheral ICs can be reduces and the like.
Such a CMOS image sensor is widely used as an imaging sensor in an imaging apparatus including a digital camera, camcorder, high-definition single-lens reflex camera, monitoring camera, car-mounted camera, and guidance system with taking advantage of superiority in low power consumption and high-speed.
In addition, recently, an image sensor having high-performance and high image quality has come to appear in which a function circuit block such as image processing is also made in on-chip together.
The mainstream of an output circuit of the CCD is one channel (ch) output using an FD amplifier having a floating diffusion layer (FD: Floating Diffusion).
On the other hand, the CMOS image sensor has the FD amplifier for each pixel and the mainstream of the output thereof is a column-parallel output type in which one column in a pixel array is selected and read out to in a column direction at the same time.
This is because sufficient driving capability is hard to obtain in the FD amplifier arranged in the pixel and therefore data rate needs to be lowered, giving a parallel processing an advantage.
As for the signal output circuit of this column-parallel output type CMOS image sensor, varieties thereof have been proposed indeed. One form thereof is a type in which an analog-digital conversion device (hereinafter, abbreviated to an ADC (analog digital converter)) is provided for each column and a pixel signal is extracted as a digital signal.
The CMOS image sensor having a column parallel type ADC installed therein is disclosed in Non-Patent Literature 1 or Patent Literature 1, for example.
There has been proposed a CMOS image sensor using a ΔΣ modulator in order to achieve a highly accurate AD conversion (e.g., refer to Patent Literature 2 and Non-Patent Literature 2).
Patent Literature 2 describe a converter performing a delta-sigma (ΔΣ) AD conversion after analog CDS. The processing technology for an image signal in this CMOS image sensor of Patent Literature 2 passes a received optical signal from a photodiode in a pixel through an analog CDS circuit arranged for each column to remove noses contained in the signal and thereafter, performs ΔΣ AD conversion.
Non-Patent Literature 2 describes a ΔΣ type AD converter having a digital CDS function therein. The technology described in Non-Patent Literature 2 can increase the number of oversampling times to reduce the noise.